1. Field of the Invention
The present invention relates to an electrowetting optical device and method of controlling voltage of the same, and more particularly, to an electrowetting optical device that selectively turns on pixels by moving liquid using an electrowetting effect and a method of controlling voltage of the same.
2. Description of the Related Art
Electrowetting is a type of electrocapillarity involving a contact angle change caused by an interfacial tension change arising by interfacial electric charge. In particular, the term electrowetting is used when a thin insulation layer is formed on an interface to increase the electric potential level of the interface.
Since an electric field is used in a method of controlling a tiny amount of liquid or fine particles contained in liquid using the electrowetting effect, wiring lines and electrodes formed integrally with a biochip or microfluidic device can be used in the controlling method. Further, in the controlling method, a tiny amount of liquid can be moved at a high speed of about 1 cm/s, and the movement of liquid can be controlled using a low voltage (assuming less electricity). For these advantages, the controlling method using the electrowetting effect may be used in conjunction with micromachining for the next generation of display devices.
FIG. 1 is a schematic view illustrating a conventional electrowetting optical device 10 of the prior art, and FIGS. 2A through 2C are cross-sectional views illustrating the movement of an oil layer when a voltage is supplied to the conventional electrowetting optical device 10 of the prior art.
Referring to FIG. 1, the electrowetting optical device 10 includes a cell 11 that is surrounded by a light-incident surface 11a, a light-exit surface 11b formed opposite to the light-incident surface 11a, and side surfaces 11c and 11d, an electrode 12 formed on the light-incident surface 11a, an insulation layer 13 formed on the electrode 12, an oil layer 14 filled in the cell 11 to a predetermined thickness and contacting the insulation layer 13, an aqueous solution layer 15 filled in the cell 11 and contacting the oil layer 14, a power source 16 electrically connecting the aqueous solution layer 15 and the insulation layer 13, a switch 17 turning on and off the power source 16 and a light source 18 disposed outside the cell 11 for emitting light onto the cell 11.
When the switch 17 is turned off as shown in FIG. 1, the oil layer 14 covers the top surface of the insulation layer 13 and the aqueous solution layer 15 is separated from the insulation layer 13 by the oil layer 14, since the insulation layer 13 is hydrophobic.
The oil layer 14 is a light-blocking layer, and the aqueous solution layer 15 is a light-transmitting layer, such that light emitted from the light source 18 cannot reach the aqueous solution layer 15 since the oil layer 14 blocks the light entering from the light incident surface 11a. 
Referring to FIG. 2A, when the switch 17 is turned on, an electric potential is formed on the insulation layer 13, thereby changing the insulation layer 13 from hydrophobic to hydrophilic. Thus, the affinity between the insulation layer 13 and the oil layer 14 decreases, and instead the affinity between the insulation layer 13 and the aqueous solution layer 15 increases, thereby making the oil layer 14 unstable. For this reason, the oil layer 14 concentrates to departing from the unstable state, and the contact area between the insulation layer 13 and the oil layer 14 reduces to a minimal amount.
As a result, the aqueous solution layer 15 can make contact with the insulation layer 13, and light emitted from the light source 18 can pass through the aqueous solution layer 15 and the light-exit surface 11b. When the aqueous layer 15 has one of red, green, and blue colors, light passing through the aqueous layer 15 can have the same color as the aqueous solution layer 15. When each pixel of the electrowetting optical device is configured with three cells respectively having red, green, and blue aqueous solution layers, an image having various colors can be realized by selectively applying a voltage to the cells.
FIGS. 2A through 2C are cross-sectional views illustrating the movement of the oil layer 14 when a voltage is supplied to the electrode 12. FIG. 2A illustrates when the oil layer 14 is moved to the left side of the cell 11, FIG. 2B illustrates when the oil layer 14 is moved to the right side of the cell 11, and FIG. 2C illustrates when the oil layer 14 is moved to both left and right sides of the cell 11. That is, when a voltage is applied to the electrode 12, it is difficult to predict the moving direction of the oil layer 14. Moreover, when the oil layer 14 is moved to both sides of the cell 11, as shown in FIG. 2C, the amount of the oil layer 14 may be different on both sides of the cell 11.